The present invention is directed to image processing and in particular to enhancing the legibility of text in document copies that photocopiers produce.
The vast majority of documents that are photocopied consist primarily of text, and the usefulness of the resultant copy depends greatly on the text's legibility. Unfortunately, many factors in the photocopying environment conspire to reduce text legibility. One of these is that the text may be embedded in a background image, and the copying process may tend to lose the contrast between text and the image and thereby impair the resultant copy's legibility. Another common difficulty arises when a document original is printed on two sides, or there is another document located behind it. It often happens in such situations that the text from the reverse side or other document "bleeds through," making the front-side text hard to read.
Photocopier manufacturers have accordingly attempted to deal with this problem by so processing the scanned digitized image as to emphasize the delineation between text and image or background. Common among the approaches to solving this problem is the use of digital filters that so process the digital image as to emphasize differences between a pixel's value and those of pixels in its immediate neighborhood. This has a tendency to darken text characters' outlines and thus enhance legibility.
But it also has a drawback. Although it does tend to enhance legibility, it also emphasizes annoying aliasing artifacts, which result from digital processing's necessarily discrete nature.